I don't know anything about the Isuzu diesel. But I have looked at a lot of the Holiday Ramblers. When I bought my diesel bounder in '94 the HR's were way out of my price range. As I remember it, one of their claims to fame was the aluminum sides.

Since you mentioned siding, heres a tidbit....The filon siding that just about all motorhames use now will strat to delaminate in 10 years or less. The long rigs with a lot of cantilevered body past the rear wheel are worse. Over time, that body flexes and bends at teh rear axle which in time pops the laminated filon loose. Look at just about any rig that is 8+ years old and you'll see waves in the siding. That's the filon delaminating.